1. Field of the Invention
The present invention relates to a method of selecting a vocoder in a code division multiple access (CDMA) mobile communication system. Specifically, this invention is a vocoder selection method where, after a shelf, a slot, and a vocoder are sequentially selected when a call occurs, the selected slot and other slots are compared in their numbers of frame offsets identical with the frame offset of the call to detect a slot containing the minimum number of the frame offsets, therefore preventing the same frame offsets from being drawn together in a specific slot in a CDMA mobile communication system.
2. Discussion of Related Art
When selecting a vocoder located at a specific slot for allocation of a call in a CDMA mobile communication system, the value of the frame offset of the call which was allocated to the slot lastly is detected and compared with the frame offset of a call which will be allocated. If the two frame offsets are identical, a vocoder located at the next slot is selected. Essentially, even though the selected slot contains many frame offsets identical with the frame offset of a present call to be allocated, if the frame offset of the call which will be allocated is different from the frame offset of the last call, the vocoder in the selected slot is selected for the present call. There is a problem that same frame offsets tend to be drawn in one specific frame offset.
For example, it is assumed that frame offsets of calls in a slot, which is selected and is in process, are as follows: 0.fwdarw.2.fwdarw.0.fwdarw.3.fwdarw.0.fwdarw.4.fwdarw.0.fwdarw.1, where there are four "0" frame offsets, and "1" is allocated to the last call. Even though another slot has "0" frame offset less than four, if the frame offset of the call which will be allocated is "0" which is different from the last call frame offset "1", the vocoder located at the presently selected slot is selected for the call.
When the same frame offsets come together in a specific slot as described above, delay can occur while processing data within 20 ms in the CDMA mobile communication system, thereby deteriorating the quality of sound in communication and bringing about overload in a base station caused by the overload in a specific slot.